The present invention refers to arm rests for motor vehicle seats, particularly front seats having a backrest with lateral sides, of the type comprising an elongated body and a load bearing structure incorporated in the body and including swinging mounting means of the arm rest comprising a connecting element adapted to be fixed relative to a lateral side of the backrest, a tubular end portion of the load bearing structure oriented transverse to the body, and a shaft coaxially inserted within the said tubular end portion and having one end projecting from the body and secured to the said connecting element so as to allow rotation on the said shaft of the tubular end portion of the load bearing structure between a raised position and a lowered position of the arm rest, and stop means for stopping rotation of the arm rest in the said raised and lowered positions.